1. Field of the Invention
The present invention relates to an optical source generator for wavelength division multiplexing optical communication systems.
2. Description of the Related Art
Recently, research has been actively carried out regarding wavelength division multiplexing (WDM) using a multi-channel optical source in order to increase transmission capacity in the optical communication field. Here, the multi-channel optical source in the WDM system makes use of an approach which allocates an optical signal to be transmitted to an assigned wavelength. Currently, a semiconductor laser is generally used as the optical source of the transmitter in the WDM optical communication system. However, this semiconductor laser optical source needs a precise wavelength control, because the laser should be precisely controlled to operate at a wavelength recommended by the International Telecommunication Union (ITU), and because an output wavelength is controlled by means of a temperature control. If a multi-channel optical source is needed, the number of wavelengths to be controlled increases, which complicates the control operation. In addition, if a multiplexed multi-channel optical source is needed, a separate multiplexer is required.
To solve these problems, a multi-wavelength laser optical source generator has been developed that employs two 1×N arrayed wave-guide gratings and an erbium-doped fiber amplifier.
FIG. 1 shows a construction of a conventional multi-wavelength laser optical source generator. As shown in FIG. 1, in the conventional multi-wavelength laser optical source generator, N ports of a wavelength division multiplexer 10 are interconnected with N ports of a wavelength division demultiplexer 20 by a plurality of optical fibers 30, and a plurality of optical fiber amplifiers 40 are disposed on the plurality of optical fibers 30. A multiplexed port of a wavelength division multiplexer 10 is interconnected with a multiplexed port of a wavelength division demultiplexer 20 through a wide band pass filter (OBPF) and an optical fiber.
Spontaneous emissions generated from the optical fiber amplifiers 40 by pumping operation of a plurality of pump lasers 60, which are connected to the demultiplexed ports of the wavelength division demultiplexer 20, are lased as the lights are infinitely circulated along to the wavelength division multiplexer 10, the OBPF 50, the wavelength division demultiplexer 20 and the optical fiber amplifiers 40, in turn. Here, the OBPF 50 is used to select a passband of an arrayed wave-guide grating having a periodical property. Further, between the OBPF 50 and the wavelength division demultiplexer 20 is disposed a coupler 70 which can be used as a multi-wavelength optical source. Between output terminals of the optical fiber amplifiers 40 and demultiplexed ports of the wavelength division multiplexer 10 are disposed a plurality of modulators 80 having N in number, each of which can be used as a single wavelength optical source.
However, if the number of optical sources needs to be increased in the conventional optical source generator, for example if the number of basic optical source channels needs to be increased from N to 2N, another optical source generator is required. That is to say, when using conventional multi-wavelength ring laser optical sources, an additional N optical sources must be provided using optical fiber amplifiers, two 1×N arrayed wave-guide gratings must also be provided, and temperature must be controlled so that the arrayed wave-guide gratings can be operated. Therefore, it is not likely that reduction of an installation expense, improvement of installation efficiency, etc. can be achieved when there is such an increment in the number of the optical channels.